Method of grinding hobs



Jan. 13, 1931. c. G oLsoN 1,788,737

- METHOD OF GRINDING HOBS I 5 Sheets-Sheet i Filed April 15, 1929 J55. 13, 1931. .q. G. OL SON 1,788,737

METHOD OF GRINDING HOBS I Filed April 15, 1929 s Sheets-Sheet; 2

Jan. 13, 1931. g, OLSON 1,788,737

METHOD OF GRINDING HOBS Filed April V15. 1929 3 Sheets-Sheet 3 (Zwl 0/50 left hand hob.

Patenteddan. 13, 1931 UNITED s rA TEsf CARL G. OLSON, OF CHICAGO. ILLINOIS, ASSIGNOB TO ILLINOIS TOOL WORKS OF PATENT OFFICE 4 CHICAGO, ILLINOIS, A CORPORATION 01' ILLINOIS METHOD OF GRINDING HOIBS Application filed April 15, 1929. 88118.1 No. 855,307.

My invention relates to methods of hob grinding and particularly to methods of grinding hob teeth to properly shape said teeth after hardening.

On'r of the primary objects of my present invent-mm is to provide an improved method wherebvhob teeth may be ground with a minimum amount of. adjustment and shifting of the work. I

Ordinarily hob teeth have sloping sides to conform with the selected pressure angle, and owing to this and the fact that the-teeth are arranged in the form of a helix. the-matter of changing the grinder from one side of the teeth to the opposite side involves adjustment which-is somewhat complex. In the case of straight ga'shed hobs still. another factor must be taken into consideration due to the fact that the body of the tooth is not at right angles to the gash. I Thus my present invention contemplates the provision of a method of grinding whereby these changes and adjustments may be accomplished in a simple and reliable manner.

The above mentioned and other objects w ll he more apparent by referring to the accompanying drawings wherein;

Figure 1 is an assembly view of the principal parts of a machine by means of which my improved method of grinding may be practiced. Some of the parts are shown in vertical axial section in ordert'o better reveal the functional characteristics of the device.

Figure 2 is a rear elevation of the parts of the machine shown in Figure 1. This View shows the grinder head-and parts immediately supporting it and in dotted lines indicates an alternate position whichthe grinder head may occupy for grinding a hob of the opposite lead or ure illustrates the change from a right to a Fi 3 is a plan view of the grinder head and its support. This figure also shows the hob and a portion of the hob spindle.

Figure 4 is a sectional elevation on the line 4-4 Figure 3.

Figure 5 is a sectional elevation on the. line i lief in the 55 Figure 4.

'of the hand. In other words this fig.

Figure 6 is a perspective view of the grinder head, adjusting shim, tool "rest and anchor'belt, the-parts being separated to show their construction and to indicate their rela tionship in the assembled machine.

Figure 7 is a diagrammatic view illustrating the reasons for changing the elevation of the grinder in changing from one side of the hob teeth to the other when treating a straight gash hob. This adjustment may for con venience be termed the vertical shift.

on ,a arger scale the reasons for making the vertical shift or adjustment.

Figure 9 is detail view partially diagram matic showing the relation of the grinding wheel to the hob in the different positions.

Figure 8 is also diagrammatic and shows .Like numerals denote like parts throughout the several views.

The hob 1 is supported upon the hob spindle 2. In Figures 1, 3. and 4 a spiral ash hob is illustrated while in the diagram igures 7 and 8. a straight gashed hob is illustrated. The hob spindle has a rotary movement about its own axis and also a longitudinal or axial movement lengthwise of its axis and also a radial movement for moving the hob bodily toward and from the grinding wheel in conformity with the relief hob teeth. These movements may be accomplished indifferent ways without ex.- ceeding the scope of my invention. In the illustrated case the mechanism for roducing these movements of the hob i's ike the one shown in my earlier Patent Number 1,575,713. It will be suficient for the present purpose to say that the hob spindle is journaled in two bearings 4, 6 mounted in a frame 7 closed by a cover 8., The journal 6 is internally threaded and constitutes a lead nut in which works the threaded end portion 10 of the hob spindle. This forms the lead screw for moving the hob axially in conformity giigh the thread angle or helical lead of the The housing 7 rocks or rolls upon its support, for movmg the hob bodily toward and mm the grinder in accordance with the rehob teeth. One part 12 of the support is shown in Figure land a steel tape 14 is inserted between the housing and its support for holding the housing in position as explained in my aforesaid patent.

The hob. spindle is rotated bya gear 16 which is fastened to it and meshes with wide face driving pinion 18. This is driven by suitable gearing including a pinion 20. The pitch circle of pinion 18 is tangent tothe plane of the support 12.

Now referring to the grinderand its support: a tool carriage 22 slides upon a guide 24 arranged crosswise of the hob spindle. .It is controlled'by a feed screw 26. A cross carriage 28 is slidingly mounted on the carriage 22 and is controlled by an adjusting screw 30. A tool rest or base 32 is supported on carriage 28. It pivots about a pin 34 and has arcuate slots 36 for receiving clamping screws 38 by which the tool rest may be held in the proper angular adjustment. This determines the angle of obliquity between the hob spindle and the grinder spin dle hereinafter described.

Above the tool rest is a grinder head and this'comprises a block shaped shank 40 and a sleeve 42 which forms an extension or bracket from it, and holds a quill 44.' The spindle 46, .which sup orts the grinder wheel 48, is journaled in t e quill and driven bya sheave 50 and belt 52. For clearance and other reasons the sleeve 42 and grinder spindle axis are arranged at an angle to the hob spindle axis when the shank block is at right angles to it as shown in Figure 3. In the form shown the top and bottom surfaces of the shank block 40 are parallel.

The quill is slidable longitudinally in a sleeve and is held in adjusted position by a set screw 54.

The shank 40 rests ordinarily upon a wedge block or plate 56 shown separately in perspective in Figure 6. This block rests upon the top of the tool rest- 32 and has a central aperture 58 for accommodating an anchor bolt 60 by which the parts may be clamped together. At the lower end the anchor' bolt or clamping screw 60 is suitably fastened to the support 32 by means of a pin 62 as best shown in Figures 4 and 5. The shank 40 is centrally apertured. to ac-' commodate the bolt and is held down by a nut 64 screwing on the upper end of the bolt.

The wedge block has a slot 66 at each end for engaging locating pins 68 projecting upward from the tool rest 32. These pins prevent the wedge block from shifting in any direction upon the surface of the tool rest.

Channels 70 are formed in the u per and lower surfaces of the shank 40 an 7 these fit over the rounded upper ends of the locating pins. The construction is' such that the grinder head may change its angular position upon the top of the tool rest in accordance with the shape of the wedge block but will be held by the pins against shifting in a direction transverse to channels 70. These 4 channels extend transversely to the hob spinplane passing throughthe hob axis and also to a horizontal plane passing through the hob axis. lVith a given shaped grinding wheel the first angle varies in accordance with the pressure angle of the teeth and the second angle varies with the helix angle of the hob. In preparing for grinding the parts are so adjusted that the median line of the shank of the grinder head will pass through the center of the space between the two lines of contact of the grinder on the hob teeth. In other words. when the grinder acts upon a tooth and-when acting upon'the tooth on the opposite'side of said space will make line contact with the latter tooth and the grind- .ing machine will he so adjusted that the median line of the grinder head shank will lie half way between these two lines. The advantage is that when the grinder head is turned over to act upon the opposite side. of the hob teettgit will not be necessary to make an adjustment of either the hob or the grindi ng wheel in a direction lengthwise of the hob. This principle is illustrated diagrammatically in Figure 9 wherein M represents the median'line. It is the same as the upper portion of the line 4-4 in Figure 3.

When one side of the hob teeth have been ground the grinder head is lifted off and turned over so that it will be reversed from the posltion shown in full lines in Figure 9 to the position shown in dotted lines in said figure. This is accomplished by first removing the nut 64 from the anchor bolt 60. then lifting off the grinder head and turning it over and then securing the parts in the new position by reapplying the nut 64. In the 'case of the smaller single thread hobs this reversing of the grinder head is made Without disturbing the wedge block and while this imports a slight discrepancy theoretically the inaccuracy is so small as a. practical matter that it is negligible. In the case of hobs of larger sizes or'larger helix angles and in hobs of double thread another factor must be taken into consideration. This will be understood by reference to the diagrams, Figures 7 and 8, which show a straight gash hob. An adjustment must he made which will cause the grinder to commence its work at the front of the hob tooth when the grinder is reversed. In the diagram the line FF represents the front of the teeth facing any given gash. The line AA represents a normal to the line of contact when the grinder is on one sideof the space, and the line BB represents a normal to the line of contact when the grinder .is on the other side of the space. If we assume that the line FF lies in a horizontal plane it is evident that if the grinder is at first located at the elevation indicated by the center of the full line circle 0 it must, when reversed, be lowered tothe extent indicated by the center of the dotted line circle C. For the sake of explanation this lowering'may'be referred to as the vertical shift, although it will be understood that the term vertical is employed because in the illustrated embodiment of the invention the shift would be vertical. T 0 express the principle universally it would be more accurate to say that there is a relative adjustment represented by a narrow angle centered at the hob axis and lying in a plane perpendicular to the axis of the hob. In my machine this vertical shift is accomplished in a-very simple and effective manner, and thatis by substituting a thinner wedge block when the grinder head is reversed. Byemploying this expedient the grinder head will automatically come both to the correct angles and to the. correct elevation and will cause the grinder to make the necessary horizontal shift (lengthwise of the hob) without requiring any other manipulation of the machine on' the part of the operator. Thus in my machine, in grinding straight gash hobs. by merely turning the grinder head over and substituting a wedge block of diiferent thickmess the line of contact of the grinder will be shifted both vertically and horizontally and the grinder will'be brought to the position required by the pressure angle and by the helix angle of the hob.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

The method of grinding a hob having a spiral series of relieved teeth which includes the steps of positioning a grinding wheel with its axis of rotation in a plane substan-- tially normal to the hob helix, rotating the wheel and the hob and effecting relative reciprocation between the wheel and the hob to eifect the grinding of one side of each of said relieved teeth, reversing the positionof the wheel to cause the latter to assume a osition substantially degrees removed rom the first position, and vertically adjusting the position of the grinding wheel contemporaneously with the reversal thereof so 'as to effect the proper tangential en agement of the grinding wheel with the si es of the hob teeth at the front thereof.

In witness whereof, I have hereunto subscribed my name.

- CARL G. OLSON. 

